The present invention claims priority from Japanese Patent Application No. 10-374508 filed Dec. 28, 1998, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a radio data communication system in which in data communication utilizing a radio transmission channel, data communication processing on the center side can be continued even if a radio channel is disconnected and data communication is interrupted, by obtaining information on a period where data communication is interrupted, and more particularly, to a radio data communication system in a transportation system such as subway, i.e., a radio data communication system in which a radio communication terminal moves to a radio data communicable section (station or the like) and a radio data incommunicable section (tunnel or the like) alternately, and a period to pass through the radio data incommunicable section can be predicted with a certain level of precision.
2. Description of Related Art
A conventional radio data communication method will be described with reference to FIG. 2. In FIG. 2, a mobile gateway 202 stores the content of data communication with an application server 201 without changing the communication speed. A network 203 uses an existing radio communication network (e.g. PIAFS: PHS Internet Access Forum Standard). Data communication is performed by using a predetermined communication procedure between the application server 201 and a radio communication terminal 204.
The conventional mobile gateway 202 stores data communication content without consideration of communication speed with the application server 201. The mobile gateway 202 has a function to store the content of data communication when communication with the radio communication terminal 204 is interrupted, and when the communication with the radio communication terminal 204 is restarted, simply transmit the stored content of data communication to the radio communication terminal 204. This prevents duplexing of communication procedure (repeating communication from the start between application server and terminal) due to disconnection of communication with the radio communication terminal 204.
However, the conventional radio data communication system has following problems.
A first problem is that in a case where the radio communication terminal 204 becomes incommunicable in some period, the mobile gateway 202, which is not informed of the incommunicable period, cannot change the speed of communication with the application server 201.
A second problem is that in a case where the radio communication terminal 204 becomes incommunicable in some period, as the mobile gateway 202 stores the content of communication from the application server 201 without changing the communication speed, if a predetermined period for each application program has elapsed, the application server 201 cannot continue the sequence of communication.
In a radio data communication system having the conventional mobile gateway 202 with the first and second problems, the transmission efficiency is degraded and the application server 201 is overloaded in the following case. As shown in FIG. 12, radio data communication may include an incommunicable section when a radio communication terminal 1207 passes through a tunnel. The time for the terminal to pass through the incommunicable section is an incommunicable period. Conventionally, this incommunicable period is not known on the center side, and the application server suspends communication by using a timer unique to the application program, and enters communication non-restorable status. Accordingly, when the radio communication terminal 1207 has passed through the tunnel and become a communicable status, the communication before the suspension cannot be continued, and communication and application program must be started again from the initial status. Such problem frequently occurs when the terminal moves by subway where communicable and incommunicable sections repeatedly come alternately in a short period. However, in movement by subway, the period of movement is stable in comparison with movement by private car and on foot, and a period between entrance and exit of a tunnel can be easily predicted. By utilizing these factors, a period notification device 1205 which transmits period information on a period for a train to pass the tunnel (the period from a point where the train enters the tunnel and a point where the train goes out of the tunnel and enters a communicable status) by a weak radio wave is placed around the entrance of the tunnel. A radio communication terminal 1207 receives the period information and sends the period information to a mobile gateway in a center 1201 in radio data communication. The mobile gateway controls (delays) the communication time with the application server based on the period information, to prevent the application server from entering a communication nonrestorable status as in the case of conventional system.
The present invention has its object to provide a radio data communication system in which a mobile gateway continues communication with an application server in expectation that a radio communication terminal restores connection after elapse of incommunicable period.
According to one aspect of the present invention, in data communication utilizing a radio transmission channel, data communication processing can be continued on the center side even if data communication is interrupted due to disconnection of radio channel, by obtaining a period where data is interrupted in advance. More specifically, in a situation where a radio communication terminal moves through a radio data communicable section (station or the like) and a radio data incommunicable section (tunnel or the like) alternately as in subway transportation and a period to pass the radio data incommunicable section can be predicted with a certain level of precision, a device to transmit information on a period necessary for passing the tunnel or the like is placed in front of the tunnel, then the mobile gateway of the present invention reduces the communication speed, and performs communication with an application server on the center side taking the place of the radio communication terminal (client) in correspondence with the period. Thus the communication between the application server and the client application program can be continuously performed without time-out in the application server on the center side.
That is, provided is a radio data communication system comprising: an application server provided in a center; a plurality of radio communication terminals each performs data communication with the application server by utilizing a radio communication channel while moving; means for providing predicted disconnection period information, on radio channel disconnection caused when the radio communication terminal moves to a specific position; delayed communication means for, when it is predicted that the radio communication terminal moves to the specific position, performing communication processing taking the place of the radio communication terminal for a period indicated by the disconnection period information, responding to the application server, storing processed communication content, and when the period indicated by the disconnection period information has elapsed, transmitting the stored communication content to the radio communication terminal.
It is preferable that the delayed communication means has means for reducing the speed of communication with the application server when the delayed communication means performs the communication processing taking the place of the radio communication terminal and when it transmits the stored communication content to the radio communication terminal. In this case, it is preferable that the delayed communication means has means for determining a period where the speed of communication with the application server is reduced, based on the period indicated by the disconnection period information and a period necessary to transmit all the stored communication content to the radio communication terminal. Otherwise, it may be arranged such that the delayed communication means has means for determining a period where the speed of communication with the application server is reduced by always monitoring the remaining amount of stored communication content.
It is preferable that the delayed communication means has means for monitoring the content of communication between the application server and the radio communication terminal and recognizing the type of application program used in the communication, and means for selecting a communication response in correspondence with the recognized application program.
The delayed communication means is realized as a function of the mobile gateway to connect a network to provide a radio circuit communication channel to the radio communication terminal in the center with the application server.
The means for providing the disconnection period information includes means for transmitting the disconnection period information, by a radio wave receivable for the radio communication terminal, around a position where the radio communication channel is disconnected. The radio communication terminal includes means for notifying the center side of received disconnection period information. Further, the delayed communication means includes means for extracting the disconnection period information from the notification means. In this case, the radio communication terminal includes means for suspending data communication with the application server in accordance with notification of disconnection period information to the center side. Further, the radio communication terminal has a timer for restoring the data communication when a period indicated by the disconnection period information has elapsed, or the radio communication terminal has means for monitoring the intensity of radio wave from a base station and restoring the data communication.
Further, it may be arranged such that the means for providing the disconnection period information has means for detecting an identifier unique to the radio communication terminal, sent by the terminal, around a potion where the radio communication channel is disconnected, and means for notifying the delayed communication means of the detected identifier and the disconnection period information. The identifier may be detected by the means for providing the disconnection period information from a signal used by the radio terminal device for communication, or may be detected as a response to connection period information.
That is, it may be arranged such that the means for providing the disconnection period information includes means for transmitting the disconnection period information by a radio wave receivable for the radio communication terminal, and wherein the radio communication terminal includes means for returning an identifier of the radio communication terminal when the disconnection period information has been received. In this case, it may be arranged such that the radio communication terminal includes means for suspending data communication with the application server in accordance with return of the identifier of the radio communication terminal. It may be arranged such that the radio communication terminal has a timer for restoring the data communication when a period indicated by the disconnection period information has elapsed, or the radio communication terminal has means for monitoring the intensity of radio wave from a base station and restoring the data communication.
It may be arranged such that the radio communication terminal includes means for detecting a position of the radio communication terminal and means for notifying the center side of the detected positional information. Further, the means for providing the disconnection period information includes memory means in which position where radio communication channel disconnection is predicted and its disconnection period information are stored. Further, the delayed communication means includes means for extracting the positional information notified from the radio communication terminal and means for searching the memory means to obtain corresponding disconnection period information based on the extracted positional information.